Cirrus Clouds Optical Properties Measured With Lidar At Camagüey, Cuba.

Abstract

Cirrus clouds play a key role in the earth’s radiative budget. To understand and quantify its impact on earth’s atmosphere radiative transfer it is necessary to have information about its optical properties. Such a knowledge is necessary both for comparison with other datasets of cirrus measurements as well as for modeling its role on radiative transfer. Cirrus clouds were measured by lidar at Camagüey (21.4º N, 77.9º W) between 1993 and 1998. We derived the extinction coefficient profile using a set of eight constant Extinction to Backscattering ratio conversion coefficients. Our lidar measurements are biased because we normally conduct measurements on clear nights to the naked eye. As result of the bias our cirrus lidar dataset is mostly representative of thin and subvisible cirrus. Making use of such fact we selected the most appropriated conversion coefficient considering the frequency of occurrence of the calculated optical depth values among the ranges attributed to thin and subvisible cirrus clouds. The 131 measurements were classified in three groups according to their optical depth (τ): opaque (τ > 0.3), thin (0.3> τ >0.03) and subvisual (τ > 0.03). The mean values for each one of the three groups were 0.498 ± 0.268, 0.074 ± 0.047 and 0.016 ± 0.010 respectively. The mean values of extinction along the complete cirrus vertical depth were derived too. The comparison with results reported at midlatitudes was conducted, the results are discussed.